The invention relates to rapier looms generally, and more particularly to rapier looms having adjustable picking mechanisms to accommodate different yarn properties.
In some rapier looms of the relevant kind rapier movement is produced by means of flexible tapes and oscillating tape wheels, the tape wheel drive being coupled with the loom main shaft and being by way of so-called three-dimensional crank drives (see DE-PS 3 029 642=MR 170). The rapier heads have wedge clamps for the weft yarn which enable the yarn to be taken over automatically at the shed entry (by the giver) and at the center of the shed (by the taker) without automatic acutation of the clamps. The actuating levers provided to open the clamps serve to open the clamps by means of cams at the rapier head reversal positions outside the shed in order that fibres which have remained stuck may be cleared, for example, by means of blowing nozzles (also, in the case of the taker, to release the weft yarn).
The automatic yarn clamps of the rapier heads have the advantage of simplifying rapier looms, but disturbances may occur because of the kind of yarn. For example, when a stiff heavy yarn is being processed, there may be mistransfers from the giver to the taker. At yarn transfer the rapiers experience maximum acceleration in the outwards direction of movement because of the drive by the three-dimensional crank system; consequently, a maximum inertia force is effective in the weft yarn of the giver. After the reversal position this inertia force is directed oppositely to the direction of movement during the return of the giver, with the possibility that the weft yarn may slip out of the yarn clamp before being taken over by the taker and thus be unable to be transferred. When endeavours are made to obviate this disadvantage by increasing the clamping force of the giver clamp, a new problem arises, for the yarn may then be damaged, for example, torn, when it is pulled out of the giver by the taker with a force which is bound to be increased because of the increased clamping force.
The problems described relate also to looms having rigid rapiers. The invention therefor relates to such looms as well.